Most 240Z owners come into this expecting a quick answer - pull up a fitment chart, grab whatever's in stock and move on with their day. It's a little more involved than that, though. The car is over 50 years old at this point, dealership support has been gone for decades, and the information floating around on forums is about as reliable as a coin flip. One source recommends a Group 24, another swears by the 24F and a third throws the 51R into the combination - and after an hour of digging, most owners come away with more questions than they started with.
The wrong terminal orientation means that the cables might not even reach their posts - it's a frustrating discovery to make in a parking lot. The cold cranking amperage matters just as much for the L24 - if you go with a rating that's too low, a cold morning will win every time. And if the dimensions aren't right, the battery won't sit right in the tray, and all that vibration against the surrounding metal eventually causes damage.
These are cars that owners have spent years caring for, and a random guess at the parts counter doesn't do anyone any favors. The right battery fit protects the electrical system from the wear that slowly builds up over years of use, and it's what gives you those confident starts that keep a classic actually on the road instead of parked in a garage waiting on a jump. For a car this well-loved, the battery is one of the easier parts to get right - as long as you go in with the right information.
Let's find the perfect battery size so your Datsun 240Z runs strong!
Table of Contents
The Group 26R Fits the 240Z Best
The "R" stands for "reverse" - the positive and negative terminals are on opposite sides compared to a standard Group 26 battery.
For the 240Z, that's actually a real problem. The factory battery cables were cut to reach the terminals at one very particular location, and if those terminals land on the wrong side of the battery, the cables just won't stretch far enough to make a connection. A loose or strained connection is the best-case scenario - the worst case is a wasted afternoon and a second trip to the parts store with a battery riding in your back seat.
The 240Z's battery tray was mostly built with the Group 26R's footprint in mind, and the fit shows it. Drop one in, and it sits flat, with the terminals pointed right at where the factory cables are already waiting. No adapters, no modifications and no creative workarounds - it just drops right in and works.
At the store, pull up the terminal layout on any battery that you're looking at - the label will tell you whether it's a reversed-terminal configuration, and plenty of batteries have it stamped right on the case as well. It's a five-second check at the shelf, and it can save you a pretty annoying round trip.
The Group 26R is a bit of a specialty size, and it doesn't always get stocked the way a standard Group 26 would be - it won't always be front and center at every auto parts store. A quick call ahead or an online inventory check will save you from a wasted trip.
Why the Right CCA Number Matters
Cold cranking amps (or CCA) is a measure of how much power your battery can push out when temperatures drop. On a freezing cold morning, your engine needs a burst of energy just to turn over, and CCA is what tells you if your battery can deliver it. Without enough of it, you're not going anywhere.
The 240Z's 2.4L inline-6 L24 engine calls for at least 550 CCA - and if anything, a little higher than that is even better. That extra headroom gives the engine a clean start with no strain, even after a full night parked out in the cold. Fall below that number and those cold mornings are going to get pretty frustrating.
Where you live plays a part in this. A driver in Minnesota or upstate New York is going to need more CCA headroom than a driver in Southern California, where the winter mornings aren't usually that harsh. If your winters are very cold, you should go a little higher on CCA instead of staying too close to the minimum. The extra headroom won't cost you a whole lot more - and it does give you quite a bit more confidence on those cold mornings.
The cheapest battery on the shelf is almost never the right battery - I see this go wrong more than anything. A weak CCA rating is what gets you stranded in a parking lot on some cold Tuesday morning, right when you least want it, and by the time you've paid for a tow and a rushed last-minute replacement, whatever you saved is long gone. Spend a little more on the right spec from the start, and you won't have to worry about it again for years.
A battery with the right CCA rating is the buy that just does its job. Get it right, and you're done with it - which frees you to have problems that are actually more deserving of your time.
The Group 51R Makes a Good Backup
The Group 51R works great as a backup choice if you can't find a 26R anywhere - it fits right into the 240Z's battery tray and (unlike the 26R) it's usually not that hard to track down at your local auto parts store.
The 51R is a touch smaller than the 26R, and there will be a little extra room in the battery tray once it sits in place. A hold-down bracket or a small shim is all it takes so it doesn't slide around. Plenty of 240Z owners have made this exact swap with no problems at all, which should put your mind at rest if you're still on the fence about it.
One detail worth a double-check with the 51R is the terminal layout. Because both the 51R and the 26R use a reversed post arrangement, the orientation should match up. But you'll still want to confirm your existing cables reach the right posts without any strain. On most 240Zs, the factory cables are already long enough for this. Even so, a quick look under the hood first can save you from an unnecessary run to the store.
The cold cranking amps are worth a look as well. The 51R won't always match the 26R in CCA, and the difference can affect how your engine fires up on a cold morning. As long as the CCA falls within a decent range for your climate and driving habits, the 51R will manage the job just fine.
Move the Battery to the Back
The 240Z has always leaned a little nose-heavy. On a casual weekend drive, that front-heavy balance doesn't give you much issue. Get it into a corner with any intent though, and you'll start to feel it fighting back.
A rear battery relocation is one of the most popular modifications on the 240Z for a reason. Move the battery to the back of the car, and it pushes a decent chunk of weight rearward, and the difference it makes to the car's balance is pretty dramatic. The front end feels noticeably lighter and quicker to rotate, and the car as a whole feels more responsive and alive under your hands. For anyone who takes their 240Z to the track or just loves a canyon road, this modification is worth doing.
The process itself takes a little bit of planning. At a minimum, you'll need a battery relocation kit, longer cables to run from the rear hatch area forward to the engine bay, and a ground connection mounted at the rear of the car. That rear ground connection is where plenty of owners cut corners, and a weak or missing one will cause all kinds of electrical gremlins that are a real pain to track down. Do yourself a favor and don't skip it.
Before taking on this project, it's worth being honest with yourself about how you actually drive the car. A weekend cruiser won't feel much of a difference. The real payoff is for anyone who pushes the car harder. It's also worth knowing that the longer cables have to run through the cabin, which does add a bit of extra work to your wiring setup. For some owners, that's an acceptable trade-off. For others, a well-fitted front-mounted battery is still a great option, and choosing it isn't settling.
Why AGM Batteries Are Worth the Price
Once you've already relocated your battery to the rear, an AGM battery should be on your shortlist. AGM stands for Absorbent Glass Mat - a sealed battery design where the electrolyte is held inside a fiberglass mat.
For a build like the 240Z, that sealed design earns its place in more than one way. The internals hold up much better against the vibration that you can expect from a performance engine or a rough stretch of road. A sealed case also lets you mount it on its side or at an angle with no chance of leaks at all - that flexibility matters quite a bit when you're fitting it into a tight custom rear tray.
For weekend drivers especially, charge retention is where AGM batteries earn their keep. A conventional flooded battery loses its charge pretty fast during long stretches of downtime - an AGM holds onto it much better. If your 240Z sits in the garage for a few weeks between drives, you're far less likely to walk out to a dead battery. For a car that sees more garage time than road time, that level of dependability is worth paying for on its own.
The only downside worth mentioning is the price. How much value you actually get out of it can depend on your situation - mainly, how you use the car. For a classic that spends more time in the garage than out on the road, that extra cost is usually worth it for the reassurance alone.
Battery Fit Mistakes That Most Owners Make
The battery tray in a 240Z is on the smaller side, and the fit's pretty exact - so a little prep work before a trip to the parts store goes a long way. Grab a tape measure, check which side the positive terminal needs to be on and look up the cold cranking amps that your engine calls for. Walk in with those three details and the whole trip is actually pretty easy.
Terminal placement is one of the most common mistakes I see with this car. A battery can fit in the tray fine and still be wrong for the job - if the terminals are on the wrong side, the cables just won't reach. It's a small detail to miss and ends with a return trip to the parts store.
Cold cranking amps don't get nearly enough respect from most owners, and that's where the majority of cold-start problems start. A battery with a CCA rating that's too low for your vehicle can leave you stranded on a cold morning - it's a bad time to find out you bought the wrong one.
One more point on fitment - some owners will try to force a slightly oversized battery into the tray or fiddle with the hold-down bracket to make it work. A loose battery will rattle around every time you hit a bump or take a turn. That movement puts wear and stress on the terminals and cables over time. Two minutes with a tape measure before you head out will save you from plenty of issues. Get the right size the first time and the whole swap is pretty painless!
Build Your Dream Car
At this point, you have the group size, the terminal orientation and the CCA range your engine needs - which makes the trip to the parts store much less stressful. For most builds, a standard replacement battery will get the job done just fine. If a rear relocation with an AGM setup is the direction you're headed, everything that's covered here should give you plenty to land on the right battery with confidence.
The battery is a great place to start. But on a car like this, it's just one part of a much bigger picture. A 240Z, 260Z or 280Z is a legitimately great platform - the type that rewards the attention that you put into it. Every upgrade and well-chosen part matters. Few projects feel as satisfying as when one of these cars comes together, and I'd argue few of them are as rewarding when done well.
That foundation is the mindset behind what we're all about at Skillard. We design and build custom parts made for Datsun Z cars (and only Datsun Z cars) with options that cover just about every stage of the build. Our catalog has bumpers, spoilers, aluminum door cards, center consoles and plenty more on top of that. Every piece was designed with these cars in mind from the start - not pulled from a universal fit catalog and not adapted from something else.
No matter where your Z is in the process (a full restoration or still just a rough concept), check us out at Skillard.com. Our catalog covers a fair amount of ground, and it's a great place to start if you want to get a sense of what's actually possible for your build.
